Open activity directly from notification (incoming file confirm)

(This CL is the test-fixed version of commit 95daa14e
with the same title)

Bug: 319050411
Bug: 318610752
Test: atest BluetoothOppReceiverTest
Test: manual, when an another device tries to send a file via BT,
      click the notification titled "Incoming file".
      There should be no lag when opening the activity titled
      "Accept incoming file?".
Change-Id: I3472a1170a19a420986ad8f3f32495030f1f6d18